The present invention relates to tetrapartate prodrugs. In particular, the invention relates to multi-part polymer conjugates that deliver active agents e.g., antitumor agents or the like, linked to cellular uptake enhancing moieties.
Over the years, several methods of administering biologically-effective materials to mammals have been proposed. Many biologically-effective materials, e.g., including medicinal agents and the like, are available as water-soluble salts and can be included in pharmaceutical formulations relatively easily. Problems arise when the desired biologically-effective material is either insoluble in aqueous fluids or is rapidly degraded in vivo. For example, alkaloids are often especially difficult to solubilize.
One way to solubilize biologically-effective material(s) is to include them as part of a soluble prodrug. Thus, prodrugs include chemical derivatives of a biologically-active material, or parent compound which, upon administration, eventually liberate the parent compound in vivo. Prodrugs allow the artisan to modify the onset and/or duration of action of an agent in vivo and can modify the transportation, distribution or solubility of a drug in the body. Furthermore, prodrug formulations often reduce the toxicity and/or otherwise overcome difficulties encountered when administering pharmaceutical preparations.
Typical examples of prodrugs include organic phosphates or esters of alcohols or thioalcohols. See Remington""s Pharmaceutical Sciences, 16th Ed., A. Osol, Ed. (1980), the disclosure of which is incorporated by reference herein.
Prodrugs are, by definition, largely inactive forms of the parent or active compound. The rate of release of the active drug, typically, but not exclusively, by hydrolysis of the prodrug, is influenced by several factors, but especially by the type of bond joining the active drug to the modifier. Care must be taken to avoid preparing prodrugs which are eliminated through the kidney or reticular endothelial system, etc., before a sufficient amount of the parent compound is released. By incorporating a polymer as part of the prodrug system, one can increase the circulating half-life of the drug. However, in some situations, such as with alkaloids, it has been determined that when only one or two polymers of less than about 10,000 daltons are conjugated thereto, the resulting conjugates are rapidly eliminated in vivo especially if a somewhat hydrolysis-resistant linkage is used. In fact, such conjugates are so rapidly cleared from the body that even if a hydrolysis-prone ester linkage is used, not enough of the parent molecule is regenerated in vivo. This is often not a concern with moieties such as proteins, enzymes and the like, even when hydrolysis-resistant linkages are often used. In those cases multiple polymer strands, each having a molecular weight of about 2-5 kDa, are used to further increase the molecular weight and circulating half-life.
Some ways in which these problems have been addressed are described, for example, in the above-mentioned patents, e.g. U.S. Pat. No. 6,303,569 and U.S. Pat. No. 5,965,119. These teach double prodrugs, i.e., tripartate, that comprise polymer conjugates of various biologically-effective materials, and methods of making these conjugates. The double prodrug linkages are selected to hydrolyze in vivo at a rate which generates sufficient amounts of the xe2x80x9csecondxe2x80x9d and more reactive prodrug compound within a suitable time after administration by, a trimethyl lock elimination reaction, providing improved control of the pharmacokinetics of a number of small molecule drugs, agents and the like. However, further opportunities for particularly selective targeting of diagnostic and/or therapeutic agents to tissues or cells of interest, by means of a rationally designed prodrug conjugate remain.
One particularly desirable target tissue for prodrugs is tumor tissue. It is well known that tumors generally exhibit abnormal vascular permeability characterized by enhanced permeability and retention (xe2x80x9cEPR effectxe2x80x9d). This EPR effect advantageously allows biologically-effective materials, in the form of macromolecules, e.g., protein(s) such as enzymes and/or antibodies and derivatives or fragments thereof, or the like, to readily enter tumor interstitial tissue space (see, for example, the review article by Maeda et al., 2000, J. of Controlled Release, 65:271-284, incorporated by reference herein). Certain other tissues, in addition to tumors, can exhibit this same EPR effect, under conditions of inflammation, and the like.
In brief, and without being bound by any theory or hypothesis as to the working of the EPR effect, it is believed that the EPR effect allows penetration of large molecule or macromolecule substances, including polymer-based delivery systems. This provides a substantially selective delivery of polymer conjugates into tumor tissue space, e.g., tumor interstitial space. Thereafter, however, the same EPR effect is believed to allow the released prodrug(s) and/or any newly released relatively low molecular weight, biologically-effective materials, to rapidly diffuse out of the extracellular tissue space of the targeted tissue. It is believed that if the released active agent fails to be taken up by the surrounding cells at a sufficient rate, they diffuse away from the release site in the ongoing blood or lymphatic flow.
Thus, there continues to be a need to provide additional technologies for forming prodrugs which would benefit from the multiple level prodrug concept and compensate or control for the EPR effect by allowing for more rapid update or transport of the released biologically-effective materials into tumor cells and/or cells of other tissues of interest that exhibit the EPR effect.
In one aspect of the invention, compounds of Formula (I) are provided: 
wherein:
R1 is a mono- or bivalent polymer residue, e.g., having a number average molecular weight of from about 2,000 to about 100,000 Daltons.
L1 is a bifunctional linking group;
Y1 and Y2 are independently O, S or NR7;
R2-7 are independently selected from the group consisting of hydrogen, C1-6 alkyls, C3-12 branched alkyls, C3-8 cycloalkyls, C1-6 substituted alkyls, C3-8 substituted cycloalkyls, aryls, substituted aryls, aralkyls, C1-6 heteroalkyls, substituted C1-6 heteroalkyls, C1-6 alkoxy, phenoxy and C1-6 heteroalkoxy;
Ar is a moiety which when included in Formula (I) forms a multi-substituted aromatic hydrocarbon or a multi-substituted heterocyclic group;
D is a residue of a compound to be delivered into a cell or a leaving group;
(y) is a positive integer greater than or equal to 1; and
Z is covalently linked to [D]y and selected from a moiety that is actively transported into a target cell, a hydrophobic moiety or a combination thereof.
Methods of preparing and using the inventive tetrapartate prodrugs are also provided. The methods of use include methods of treating a disease or disorder in an animal and include administering a pharmaceutically acceptable composition comprising an effective amount of a compound of Formula I, to an animal in need thereof. One particular method includes delivering a biologically active material, designated D herein, into a cell in need of treatment therewith. The method involves administering a compound of Formula I to an animal containing the cell in need of treatment and wherein the compound of Formula I is hydrolyzed in vivo extracellularly to yield: 
after hydrolysis of the polymeric residue (R1 and linker); and Formula (I-i) subsequently spontaneously hydrolyzes to 
and Formula I-(iii) Zxe2x80x94[D]y;
Zxe2x80x94[D]y then crosses the membrane of the cell, and is hydrolyzed therein to release D.